This invention relates to dual species ion implantation into gallium arsenide, and more particularly to a method of producing p- and n-type layers in GaAs by dual implantation of (Ge+Ga) or (Ge+As).
The concept of dual implantation, as proposed by Heckingbottom and Ambridge has been tested by several workers to improve the electrical activity and inhibit the diffusion of certain implant species. This approach is based on the maintenance of stoichiometry in the host lattice in order to avoid compensation due to vacancy complexes with the dopant. In the case of amphoteric (defined as producing either n- or p-type) dopants, dual implantation permits shifting the probability of lattice site occupancy by the dopant to favor either n- or p-type activity. By control and shift of defect stoichiometry of GaAs precise control of the behavior of the dopants can be attained.
Some degree of success has been achieved in the production of high carrier concentrations by dual implantation. For example, in comparison with Se single implants into GaAs, donor activity enhanced by the implantation of an equal dose of Ga has been reported. The improvement of p-type activity has been observed as a result of the dual implantation of C and Ga into GaAs. Dual implants of Zn or Cd and As into GaAs have been found to decrease considerably the diffusion of the implanted Zn or Cd.
Germanium has been used as a dopant in GaAs. An understanding of the physics involved in the behavior of Ge implants is particularly important in applications where the amphoteric nature of the dopant is used to advantage. Ge has been widely used as a dopant in epitaxial layers of GaAs because of its low diffusivity. Ge has also been utilized to produce stable, reliable and reproducible ohmic contacts to n-type GaAs by methods which achieve high densities of Ge almost exclusively on Ga lattice sites. More recently, the feasibility of fabricating p/n junctions and p/n multilayers using Ge dopants in GaAs by molecular beam epitaxy has been demonstrated.
The single implants of Ge in GaAs have shown amphoteric behavior, where the conductivity type, electrical activity, and carrier mobility depend critically upon ion dose and annealing temperature. Low doses of the Ge implant appear to favor substitution into As sites, resulting in p-type activity, while high doses shown n-type activity due to preferential occupation of Ga sites by the Ge ions. These results are reported in a paper by Y. K. Yeo et al on "Amphoteric Behavior of Ge Implants in GaAs", Applied Physics Letters, Vol. 35, No. 2, pages 197-199, July 15, 1979 (American Institute of Physics).
Dual implantation is described in U.S. Pat. No. 4,137,103 by Mader et al. for "Silicon Integrated Circuit Region Containing Implanted Arsenic and Germanium". Dual implantations into GaAs which involve Ga and As ions is also disclosed by E. B. Stoneham et al, "Formation of Heavily Doped N-type Layers in GaAs by Multiple Ion Implantation", Journal of Electronic Materials, Vol. 9, No. 2, 1980, pages 371-383. The concept that Ga implants produce donors via As vacancies and that As implants produce acceptors via Ga vacancies is shown by Stolte, "Dual Species Ion Implantation into GaAs" at pages 149-157 from "Ion Implantation of Semiconductors" 1976 by Chernow, Borders, and Brice. Also from the same book at pages 585-592 is an article by M. Takai et al on "Effects of Dual Implantations and Annealing Atmosphere on Lattice Locations and Atom Profiles of Sn and Sb Implanted in GaP".
Though the experiments reported in the above references have proved the effectiveness of dual implantation in maintaining the stoichiometry in the host lattice in a broad sense, they have not investigated systematically experimental parameters such as annealing temperature and fluence to attain high electrical activity on p- and n-layers.